The formation of slime by microorganisms is a problem which commonly occurs in many systems. For example, slime commonly forms in cooling water systems, lagoons, lakes, ponds, pulp and paper mill systems, petroleum operations and in industrial lubricants and coolants. In cooling systems which employ large amounts of water as the cooling medium, the formation of slime by microorganisms is a significant and constant problem. Problematic microorganisms include bacteria, sulfate reducing bacteria, fungi and algae which produce slime in aqueous systems where such slime is objectionable from either an operational or an aesthetic point of view.
Moreover, airborne microorganisms are readily entrained in water from cooling towers because this medium is an ideal growth environment for microbiocidal growth. Various types of microorganisms flourish in the cooling tower itself while other organisms grow in such areas as the piping, the tower sump and in the passages of the cooling system. Typically, the slime acts to deteriorate towers made of wood or it promotes corrosion when deposited on metal surfaces of cooling systems. Furthermore, the slime tends to plug or foul pipes and valves and to form deposits within heat exchange surfaces thereby reducing heat exchange or cooling efficiency.
Pulp and paper mill systems also operate at conditions which encourage the growth of microorganisms resulting in similar fouling problems discussed hereinabove. Moreover, microorganisms become entrained in the paper product itself causing breakage on the paper machines which necessitates the shutting down of the paper making process. As a result, production time is lost because the equipment must be cleaned and the value of the slime containing product is reduced because of its poor quality.
Slime may also be objectionable from the standpoint of cleanliness and sanitation in breweries, wineries, dairies and other industrial plants or establishments. Moreover, sulfate reducing bacteria may become problematical in waters used for the secondary recovery of petroleum or for oil drilling in general. For example, these organisms are able to reduce sulfates present in the injection water to sulfides which in turn react with soluble iron salts to form insoluble iron sulfide. Matted deposits composed of sulfides, occluded oil and other solids are thereby produced which is undesirable since water containing such deposits when injected underground may plug subterranean formations. In addition, sulfate reducing bacteria cause the corrosion of metal by accelerating galvanic action. Accordingly, microbiological corrosion is a well recognized problem in the petroleum industry.
Moreover, ponds, lakes, lagoons or pools used either for industrial purposes or for pleasure often become suitable environments for microbial growth, especially during warm weather. Health problems including infection may result from the growth of microorganisms in recreational areas. In addition, microorganisms cause further problems during industrial storage and these organisms must be eliminated, for example, prior to use of the stored materials.
In addition, lubricants and cutting fluids are prepared by mixing organic compounds with water to produce solids, emulsions or suspensions in many metal forming operations. Bacteriological contamination of these fluids is inevitable due to the heat and dirt found in many metal working plants. These fluids must be discarded when biological contamination is too severe.
Accordingly, because of the problems discussed hereinabove in various industrial processes, numerous biocidal materials have been recommended in order to eliminate or to reduce microbial growth. Various materials have enjoyed widespread use in such applications including chlorine, chlorine dioxide, organo-mercurials, chlorinated phenols, organo-bromines and various organo-sulfur compounds. However, each of these generally useful materials is deficient for a variety of reasons. For instance, chlorination is limited by its specific toxicity for slime-forming organisms at economic levels by the pH of the aqueous medium and by the ability of chlorine to react before its full biocidal function is achieved.
Moreover, economy is a significant consideration with regard to the use of known biocides. The cost of the biocide and the expense of its applications are examples of the economic factors which must be considered. Typically, the effectiveness of the known biocides is rapidly reduced as a result of exposure to physical conditions such as temperature or a reaction with ingredients in the system which results in a loss of biocidal effectiveness. Therefore multiple doses or large quantities of expensive biocidal chemicals have heretofore been required in order to maintain control over microbial growth.
It is, therefore, a principal object of the present invention to provide microbiocidal combinations of materials which are to be added to a system at the time of their use for controlling the growth of microorganisms.
It is another object of this invention to provide an improved process for controlling microorganisms in aqueous systems such as pulp and paper mill systems, cooling water systems, and petroleum operations.
These and other objects of the novel microbiocidal combinations of materials and processes of using the same of this invention will become apparent and are further described hereinbelow.